Advanced Secondary Batteries And
Their Applications for Hybrid and
Electric Vehicles
Su-Chee Simon Wang
IEEE (Dec. 5, 2011)
1
Outline
Introduction to batteries
• Equilibrium and kinetics
• Various secondary batteries
Lead acid batteries
Nickel metal hydride batteries
Lithium ion batteries
• Applications
Electric vehicles
Hybrid electric vehicles
2
Introduction to Batteries
• Battery terminology
– Primary and secondary batteries
– Cell voltage (open circuit)
– Positive and negative electrodes
– Cathode and anode
– Power energy and charge
– Battery cell module and pack
– Charge and discharge curves
– Cycle life
3
Primary and Secondary Batteries
• Primary Battery: not rechargeable (dry
cell)
• Secondary Battery: rechargeable (lithium
ion batteries)
E
= E+ - Eoc
(Cell V)
• Battery is composed of
– Positive electrode
– Negative electrode
– Electrolyte
– Separator
– Current collectors
+
+
P
o
s
_
(Half cell V)
Pos
E
_
N
e
g
electrolyte
separator
current
collector
4
How to Determine Positive and
Negative Electrodes
5
How to Calculate Cell Voltage
• Use half cell reduction potentials (25 °C)
Electrode reaction
Li+ + e ↔ Li
Rb+ + e ↔ Rb Less stable
Cs+ + e ↔ Cs
K+ + e ↔ K
Ba+2 + 2e ↔ Ba
Sr+2 + 2e ↔ Sr
Ca+2 + 2e ↔ Ca
Na+ + e ↔ Na
Mg(OH)2 +2e ↔ Mg + 2OHMg+2 + 2e ↔ Mg
Al(OH)3 + 3e ↔ Al + 3OHTi+2 + 2e ↔ Ti
Be+2 + 2e ↔ Be
Al+3 + 3e ↔ Al
Zn(OH)2 + 2e ↔ Zn + 2OHMn+2 + 2e ↔ Mn
Fe(OH)2 + 2e ↔ Fe + 2OH2H2O + 2e ↔ H2 + 2OHCd(OH)2 + 2e ↔ Cd + 2OHZn+2 + 2e ↔ Zn
Ni(OH)2 + 2e ↔ Ni + 2OHGa+3 + 3e ↔ Ga
S + 2e ↔ S-2
Fe+2 + 2e ↔ Fe
Cd+2 + 2e ↔ Cd
PbSO4 + 2e ↔ Pb + SO4-2
In+3 + 3e ↔ In
Tl+ + e ↔ Tl
Co+2 +2e ↔ Co
E°, V
-3.01
-2.98
-2.92
-2.92
-2.92
-2.89
-2.84
-2.71
-2.69
-2.38
-2.34
-1.75
-1.70
-1.66
-1.25
-1.05
-0.88
-0.83
-0.81
-0.76
-0.72
-0.52
-0.48
-0.44
-0.40
-0.36
-0.34
-0.34
-0.27
Electrode reaction
Ni+2 + 2e ↔ Ni
Sn+2 + 2e ↔ Sn
Pb+2 + 2e ↔ Pb
O2 + H2O + 2e ↔ HO2- + OHD+ + e ↔1/2D2
H+ + e ↔ 1/2H2
HgO + H2O + 2e ↔ Hg + 2OHCuCl + e ↔ Cu + ClAgCl + e ↔ Ag + ClCu+2 + 2e ↔ Cu
Ag2O + H2O + 2e ↔ 2Ag + 2OH1/2O2 + H2O + 2e ↔ 2OHNiOOH + H2O + e ↔ Ni(OH)2 + OHCu+ + e ↔ Cu
I2 + 2e ↔ 2I2AgO + H2O + 2e ↔ Ag2O + 2OHHg+2 + 2e ↔ Hg
Ag+ + e ↔ Ag
Pd+2 + 2e ↔ Pd
Ir+3 + 3e ↔ Ir
Br2 + 2e ↔ 2BrO2 + 4H+ + 4e ↔ 2H2O
MnO2 + 4H+ + 2e ↔ Mn+2 + 2H2O
Cl2 + 2e ↔ 2ClPbO2 + 4H+ + 2e ↔ Pb+2 + 2H2O
PbO2 + SO4-2 + 4H+ + 2e
↔ PbSO4 + 2H2O
More stable
F2 + 2e ↔ 2F-
E°, V
-0.23
-0.14
-0.13
-0.08
-0.003
0.00
0.10
0.14
0.22
0.34
0.35
0.40
0.45
0.52
0.54
0.57
0.80
0.80
0.83
1.00
1.07
1.23
1.23
1.36
1.46
1.69
2.87
6
How to Calculate Cell Voltage
• Half cell reduction potentials are measured
as follows:
– Cell voltage is measured between electrode A (Cu) and
hydrogen electrode (Eoc = EA – EH2)
– The potential of hydrogen electrode in “acid” is defined as
zero volt (Eoc = EA – 0)
– The measured cell voltage is the half cell reduction
potential of electrode A
+
E
7
Calculate Cell Voltage
(Open circuit)
E?
Chemical
reactions?
Chemical
reactions?
Cu
Zn
CuSO4
ZnSO4
Cell open circuit voltage Eoc = E°+ - E°Positive electrode: Cu
Negative electrode: Zn
E°+ = 0.34 V
E = 1.1 V
E°- = -0.76 V
Zn
Cu
Eoc = 0.34 – (- 0.76) = 1.1 V (intrinsic)*
*Current: extrinsic
8
Table
Half Cell Reduction Potentials (25 °C)
Electrode reaction
Li+ + e ↔ Li
Rb+ + e ↔ Rb
Cs+ + e ↔ Cs
K+ + e ↔ K
Ba+2 + 2e ↔ Ba
Sr+2 + 2e ↔ Sr
Ca+2 + 2e ↔ Ca
Na+ + e ↔ Na
Mg(OH)2 +2e ↔ Mg + 2OHMg+2 + 2e ↔ Mg
Al(OH)3 + 3e ↔ Al + 3OHTi+2 + 2e ↔ Ti
Be+2 + 2e ↔ Be
Al+3 + 3e ↔ Al
Zn(OH)2 + 2e ↔ Zn + 2OHMn+2 + 2e ↔ Mn
Fe(OH)2 + 2e ↔ Fe + 2OH2H2O + 2e ↔ H2 + 2OHCd(OH)2 + 2e ↔ Cd + 2OHZn+2 + 2e ↔ Zn
Ni(OH)2 + 2e ↔ Ni + 2OHGa+3 + 3e ↔ Ga
S + 2e ↔ S-2
Fe+2 + 2e ↔ Fe
Cd+2 + 2e ↔ Cd
PbSO4 + 2e ↔ Pb + SO4-2
In+3 + 3e ↔ In
Tl+ + e ↔ Tl
Co+2 +2e ↔ Co
E°, V
-3.01
-2.98
-2.92
-2.92
-2.92
-2.89
-2.84
-2.71
-2.69
-2.38
-2.34
-1.75
-1.70
-1.66
-1.25
-1.05
-0.88
-0.83
-0.81
-0.76
-0.72
-0.52
-0.48
-0.44
-0.40
-0.36
-0.34
-0.34
-0.27
Electrode reaction
Ni+2 + 2e ↔ Ni
Sn+2 + 2e ↔ Sn
Pb+2 + 2e ↔ Pb
O2 + H2O + 2e ↔ HO2- + OHD+ + e ↔1/2D2
H+ + e ↔ 1/2H2
HgO + H2O + 2e ↔ Hg + 2OHCuCl + e ↔ Cu + ClAgCl + e ↔ Ag + ClCu+2 + 2e ↔ Cu
Ag2O + H2O + 2e ↔ 2Ag + 2OH1/2O2 + H2O + 2e ↔ 2OHNiOOH + H2O + e ↔ Ni(OH)2 + OHCu+ + e ↔ Cu
I2 + 2e ↔ 2I2AgO + H2O + 2e ↔ Ag2O + 2OHHg+2 + 2e ↔ Hg
Ag+ + e ↔ Ag
Pd+2 + 2e ↔ Pd
Ir+3 + 3e ↔ Ir
Br2 + 2e ↔ 2BrO2 + 4H+ + 4e ↔ 2H2O
MnO2 + 4H+ + 2e ↔ Mn+2 + 2H2O
Cl2 + 2e ↔ 2ClPbO2 + 4H+ + 2e ↔ Pb+2 + 2H2O
PbO2 + SO4-2 + 4H+ + 2e
↔ PbSO4 + 2H2O
F2 + 2e ↔ 2F-
E°, V
-0.23
-0.14
-0.13
-0.08
-0.003
0.00
0.10
0.14
0.22
0.34
0.35
0.40
0.45
0.52
0.54
0.57
0.80
0.80
0.83
1.00
1.07
1.23
1.23
1.36
1.46
1.69
2.87
9
Calculate Cell Voltage
(Open Circuit)
•
Hydrogen Fuel Cells (with hydrogen and
oxygen electrodes)
O2 + 4H+ + 4e ↔ 2H2O
H+ + e ↔ 1/2H2
Eoc = 1.23 – 0 =
•
1.23 V
0.00 V
1.23 V
Lithium Fluorine Battery
F2 + 2e ↔ 2FLi+ + e ↔ Li
Eoc = 2.87 – (–3.01) =
2.87 V
-3.01 V
5.88 V
10
How to Make High Voltage Batteries
Strong reducing
agents
Strong
oxidants
11
Cathode and Anode
• Cathode: the electrode where reduction reaction
takes place
• Anode: the electrode where oxidation reaction
takes place
Secondary battery
• During charge
– Negative electrode is the cathode
– Positive electrode is the anode
• During discharge
– Positive electrode is the cathode
– Negative electrode is the anode
12
Cathode and Anode
Secondary Battery
• During charge
– Negative electrode is the cathode
Zn+2 + 2e- Zn
– Positive electrode is the anode
Cu Cu+2 + 2e-
Charge
+ cation
Zn
Cu
anion
CuSO4
ZnSO4
• During discharge
– Positive electrode is the cathode
Cu+2 + 2e- Cu
– Negative electrode is the anode
Zn Zn+2 + 2e-
e
V
Discharge
e
Load
+
-
Cu
Zn
anion
CuSO4
ZnSO4
13
Power Energy and Charge
• Power = Voltage * Current
– 1 W (watt) = 1 V (volt) * 1 A (ampere)
– 1 kW = 1000 W
• Energy = Power * Time
– 1 Wh (watt-hour) = 1 W * 1 h (hour)
– 1 kWh = 1000 Wh
– 1 Wh = 3600 J (joules)
• Charge = Current * Time
– 1 Ah = 1 A * 1 h
– 1 kAh = 1000 Ah
– 1 Ah = 3600 C (coulombs)
14
Power Energy and Charge
• Specific power: power withdrawn per unit
battery weight
– W/kg
• Power density: power withdrawn per unit battery
volume
– W/L
• Specific energy: energy stored per unit battery
weight
– Wh/kg
• Energy density: energy stored per unit battery
volume
– Wh/L
15
Power Energy and Charge
• Examples
– AA primary alkaline battery
• 1.5 V (3 Ah)
– Lead acid SLI battery
• 12 V (50 Ah)
– Prius battery
• 202 V (6.5 Ah)
– Lithium ion battery (laptop)
• 10 V (5 Ah)
4.5 Wh
600 Wh
1300 Wh (1.3 kWh)
50 Wh
• Gasoline (tank)
– 600 kWh
16
Cell Module and Pack
NiMH Cell
1.2 V
NiMH Module
11 cells
11 x 1.2 = 13.2 V
NiMH Pack for EV1
26 Modules
26 x 13.2 = 343 V
17
Charge and Discharge Curves
Constant current charge (Ich) and discharge (Idis)
1.3
Ech
1.1
Voltage
overpotential:ηch
+
Eoc
overpotential:ηdis
0.9
+ (dis) Ech
Edis
charge
0.7
overcharge
+ (ch)
Edis
Eoc
discharge
(dis) -
(ch) -
0.5
0
0
5
SOC (%)
10
15
Time
100
0
20
25
30
DOD (%) 100
18
Charge and Discharge Curves
• Charge voltage Ech > Eoc
• Discharge voltage Edis < Eoc
• Energy efficiency = (voltaic efficiency * coulombic
efficiency) = (Edis / Ech) * (Idis* tdis / Ich* tch) < 1
• The voltage drop is caused by cell resistance
– ∆ Edis = Eoc – Edis = ηdis = Idis * R (R: broader resistance)
– ∆ Ech = Ech - Eoc = ηch = Ich * R (R: extrinsic)
Constant current charge (Ich) and discharge (Idis)
1.3
charge
Ech
Eoc
discharge E
dis
Voltage
1.1
0.9
tch
0.7
tdis
0.5
0
5
10
15
Tim e
20
25
30
19
Battery Component Resistance
Distribution
• Nickel metal hydride electric vehicle
battery (~300 W/kg)
Component
Resistance
Percentage
terminals
0.1 mohm
0.8 %
tabs
0.6 mohm
4.7 %
3 mohm
23.6 %
positive electrode
1.5 mohm
11.8 %
positive substrate
2.5 mohm
19.7 %
negative electrode
2 mohm
15.7 %
negative substrate
3 mohm
23.6 %
12.7 mohm
100 %
KOH/separators
TOTAL
20
Charge and Discharge
State of charge (SOC, %)
Depth of discharge (DOD, %)
SOC + DOD = 100
Self discharge 1.3
Ech
1.1
Discharge
– “C” rate
1C, 2C, 1/2C
Voltage
•
•
•
•
•
Edis
0.9
0.7
charge
Eoc
discharge
0.5
0
0
5
10
15
Tim e
SOC (%) 100
20
0
25
30
DOD (%) 100
21
Cycle Life
• Cycle life is the number of chargedischarge cycles a battery can deliver (has
to meet energy and power performance
targets)
• Cycle life depends on depth of discharge
and temperature
– Examples
• lead acid battery
• nickel cadmium battery
22
Outline
• Introduction to batteries
Equilibrium and kinetics, Eoc > Edis
• Various secondary batteries
Lead acid batteries
Nickel metal hydride batteries
Lithium ion batteries
• Applications
Electric vehicles
Hybrid electric vehicles
23
Equilibrium: Thermodynamics
• ∆G: Free energy change from reactants to
products during discharge (J/mole) negative value
• ∆G = - nFEoc (nFEoc: electric work) Max.
– n: Number of moles of electron transferred
– F: Faraday’s constant (96500 C/mole)
– Eoc: Open circuit cell voltage
• Theoretical Specific energy
nFEoc / total weight of reactants
24
Theoretical Specific Energy
(Lithium Ion Battery)
• Lithium ion battery half cell reactions
(+) CoO2 + Li+ + e ↔ LiCoO2 n = 1
Eº = 1 V
Theoretical specific
energy = nFEoc/ total
(-) Li+ + C6+ e ↔ LiC6
weight of reactants
Eº ~ -3 V
• Overall reaction during discharge
CoO2 + LiC6 LiCoO2 + C6
Eoc = E+ - E- = 1 - (-3) = 4 V
Eoc = 4 V
25
Theoretical Specific Energy
(Lithium Ion Battery)
• Free energy change (∆G) during discharge
∆G = -nFEoc = -1 * 96500 * 4 = - 386000 J
= -386 kJ = -107.2 Wh/mole
• Total weight of reactants
CoO2 + LiC6 LiCoO2 + C6
CoO2 91 grams
LiC6 7 + 12 * 6 = 79 grams
Total weight 170 grams (0.17 kg)/mole
• Theoretical specific energy
107.2 Wh/ 0.17 kg = 630.6 Wh/kg
• Theoretical energy density
107.2 Wh/0.055 L = 1949 Wh/L
26
Practical Specific Energy
• Practical specific energy of a battery is
significantly lower than the theoretical
value (~30%) ~ 190 Wh/kg for lithium
battery (USABC target for EV > 150
Wh/kg)
– Lower discharge voltage (Edis < Eoc)
• Voltage losses (broader resistance)
– Extra material weight
•
•
•
•
Current collectors
Terminals
Battery case
Separators
Theoretical specific
energy = nFEoc / total
weight of reactants =
630.6 Wh/kg
27
Extra Materials
• Battery current collectors and terminals
– Collect current from electrodes and interconnect to
next battery cells
– Use materials with high electric conductivity and good
heat transfer coefficient
• Battery case
– Contain all battery components
– Use materials inert with electrolyte and electrodes
– Need safety release valve with sealed cells
• Separator
– Separate positive and negative electrodes (prevent
short circuit)
– Made of insulating materials with high porosity
28
Practical Specific Energy
• Practical specific energy of a battery is
significantly lower than the theoretical
value (<30%)
– Lower discharge voltage (Edis < Eoc)
• Activation polarization losses
• Ohmic losses
• Concentration polarization losses
– Extra material weight
•
•
•
•
Current collectors
Terminals
Battery case
Separators
29
Kinetics in Batteries
• Source of voltage losses (broader
resistance)
– Electrode activation polarization losses (ηa)
• Butler-Volmer equation
– Depends on electrode reactions
– Ohmic losses (ηΩ )
• Ohm’s law (Ohmic resistance)
– Electronic resistance (electrode current collector, tabs. and
terminals)
– Ionic resistance (electrolyte and separator)
– Temperature effects
– Concentration polarization losses (ηc)
• Nernst equation
– Depends on diffusion in electrolyte and solid state
30
Charge and Discharge Curves
Constant current charge (Ich) and discharge (Idis)
1.3
Ech
1.1
Voltage
overpotential:ηch
0.9
Eoc
overpotential:ηdis
ηdis = ηa + ηΩ + ηc
charge
0.7
+
+ (dis)
Edis
overcharge
η+
Edis
Eoc
(dis) η-
discharge
-
0.5
0
0
5
SOC (%)
10
15
Time
100
0
20
25
30
DOD (%) 100
31
Kinetics in Batteries
• Sources of voltage losses (Eoc – Edis):
– Electrode activation polarization losses
• Butler-Volmer equation
P < Po
– Ohmic losses
P
Po
• Ohm’s law
– Electronic resistance (electrode current collector, tabs.
and terminals)
– Ionic resistance (electrolyte and separator)
– Concentration polarization losses
• Nernst equation
P’
Po’
P’ < P
32
Activation Polarization Losses
(Butler-Volmer Equation)
i = i0 [ e
(1−α )η F / RT
−e
− αη F / RT
]
• Current density i (electrochemical reaction at
electrode/electrolyte interface) is a function of:
– ηa :
–
–
–
–
–
Activation polarization loss
i0 : Exchange current density
α : The symmetry factor
F : Faraday’s constant
R : Molar gas constant
T : Temperature
Discharge
e
+
-
Cu
Zn
anion
CuSO4
+2
Cu + 2e Cu
ZnSO4
+2
Zn Zn + 2e
33
Effect of Rate on Discharge
C/8 Rate
2-C Rate
i = i0 [e
(1−α )ηF / RT
−e
−αη F / RT
]
Higher current higher ηa
Concentration
polarization losses
34
Concentration Polarization
Losses (Nernst Equation)
•
During discharge
Discharge
– Reaction at the positive electrode:
Cu+2 + 2e- Cu
– Reaction at the negative electrode:
Zn Zn+2 + 2e– Cell reaction:
Zn +
•
Cu+2
Cu +
V
ηc
Zn+2
Nernst equation
Eoc ,real
–
–
–
–
–
–
( A) a
RT
Ln
= Eoc ,table +
nF
( B)b
A: Concentration of Cu+2
B: Concentration of Zn+2
a and b (= 1): factor for Cu+2 and Zn+2
R : Molar gas constant
oc , real
T : Temperature
F : Faraday’s constant
E
= Eoc ,table
+
-
Cu
Zn
CuSO4
ZnSO4
RT
(Cu +2 )
+
Ln
nF
( Zn + 2 )
(If Zn+2 = Cu+2 =1M)
35
Total Voltage Losses
• Eoc – Edis = Total voltage losses (ηdis, extrinsic) =
Activation losses (ηa) + Ohmic losses (ηΩ) +
Concentration losses (ηc)
Cell voltage (V)
Voltage Los s es in Fuel Cell
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1.23 V
Activation polarization losses in electrodes
Polarization curve
Ohmic losses
Concentration polarization losses
ηdis = Eoc- Edis ~ Idis * R (broader resistance)
0
500
1000
1500
Current density (mA /cm2)
36
Model: Porous Electrode Theory
• Porous electrode theory
For a battery cell
– Butler-Volmer equation
– Ohm’s law
Power = f (1/R)
R = f (1/surface area)
Current flow
Current flow
Electrode
Pores
(electrolyte)
Current
collector
decreasing
37
MATLAB Model
38
Experimental Results
V.S. MATLAB Model
Marine Lead Acid Battery (12V, 32 Ah)
13
C/2 Test
1C Test
2C Test
C/2 Model
1 C Model
2 C Model
Voltage (V)
12
11
10
9
0.00
0.25
0.50
0.75
1.00
1.25
1.50
Time (Hours)
39
Outline
• Introduction to batteries
• Equilibrium and kinetics
Various secondary batteries
Lead acid batteries
Nickel metal hydride batteries
Lithium ion batteries
• Applications
Electric vehicles
Hybrid electric vehicles
40
Lead Acid Batteries
• Invented by Planté in 1860
• Lead acid starter batteries are enabling
technology for gasoline powered IC engine
cars
• Almost all vehicles use lead acid batteries
for starter lighting and ignition (SLI)
systems
• It is 20 billion dollars industry (total battery
industry ~ 30 billion dollars)
41
Lead Acid Batteries
• Positive electrodes
Expanded metal
– PbO2
• Negative electrodes
Cast
– Pb
• Current collectors
– Lead (or alloy) grids
1. Positive
• Separators
– Porous or glass mat
2. Negative
3. Separator
4. Tab
• Electrolyte
– 5M H2SO4 aqueous solution
5. Bus bar
6. Terminal
42
Theoretical Specific Energy
• Lead acid battery half cell reactions
PbO2 + SO42- + 4 H+ + 2 e ↔ PbSO4 + 2 H20
E°= 1.69 V
PbSO4 + 2 e ↔ Pb + SO42E°= -0.36 V
• Overall reaction during discharge
PbO2 + Pb + 2H2SO4 2 PbSO4 + 2 H20
Voc = V+ - V- = 1.69 – (-0.36) = 2.05 V
43
Theoretical Specific Energy
• Free energy change (∆G) during discharge
∆G = -nFE = -2 * 96500 * 2.05 = -395700 J
= -395.7 kJ = -109.9 Wh/mole
• Total weight of reactants
PbO2 + Pb + 2H2SO4 2 PbSO4 + 2 H20
PbO2 239 grams
Pb 207 grams
2H2SO4 98 *2 = 196 grams
Total weight 642 grams (0.642 kg)/mole
• Theoretical specific energy
109.9 Wh/ 0.642 kg = 171 Wh/kg
• Theoretical energy density
109.9 Wh/0.1 L = 1099 Wh/L
44
Practical Specific Energy
• Practical specific energy < 20 % theoretical
specific energy (171 Wh/kg) ~ 34 Wh/kg due
to:
– Voltage losses (up to 10%)
– Inactive weight (~75%)
• Current collectors
• Tabs and terminals
• Solvent (water) in electrolyte
– Low utilization of active material
USABC target for EV applications: > 150 Wh/kg
45
Charge Lead Acid Batteries
• During charge:
– 2 PbSO4 + 2 H20 PbO2 + Pb + H2SO4 (2.05 V)
– Competing reaction: 2H2O O2 + 2H2 (1.23 V)
H2
Pb
evolution
Current
Lead acid
battery voltage
2.05 V
PbO2
O2
evolution
Water
decomposition voltage
1.23 V
-1
-0.36
0
1
1.23
1.69
2
Voltage (V)
46
Electrolyte (H2SO4)
Concentration
• Overall reaction during charge
2 PbSO4 + 2 H20 PbO2 + Pb + H2SO4
The concentration of sulfuric acid increases to 5 M
• Overall reaction during discharge
Diffusion!
Power?
PbO2 + Pb + H2SO4 2 PbSO4 + 2 H20
The concentration of sulfuric acid decreases
discharge
e
V
+
anion
e
-
Pb
Pb
O2 cation
H2SO4
H2SO4
Cation: H+
Anion: SO4-2
47
Cell Capacity Under Different
Discharge Rates
4.59
Ah
5.10
Ah
5.6
Ah
6.00
Ah
48
Failure Mode
• Positive electrode
– Lead grid corrosion
PbO2 + Pb + H2SO4 2 PbSO4 + 2 H20
– Shedding
• 70% volume change from PbO2 to PbSO4 (discharge)
• Negative electrode
– Sulfation (the formation of PbSO4)
Active
material
PbSO4
Grid
Capacity available (%)
• Cycle life depends on DOD and temperature
Number of cycles
49
Outline
• Introduction to batteries
• Equilibrium and kinetics
• Various secondary batteries
Lead acid batteries
Nickel metal hydride batteries
Lithium ion batteries
• Applications
Electric vehicles
Hybrid electric vehicles
50
Nickel Metal Hydride Batteries
• Became commercially available around
1992
• Metal hydride is actually a solid phase
hydrogen intercalation electrode
• Nickel metal hydride battery has high
power and good cycle life for HEV
applications
• It is > 1 billion dollars industry (total battery
industry ~ 30 billion dollars)
51
Nickel Metal Hydride Batteries
• Positive electrodes
– Nickel hydroxide pasted onto
nickel foam or sheet substrate
• Negative electrodes
– Most common material is AB5
or MmNi3.55Co0.75Al0.2Mn0.5
where Mm is misch metal, an
alloy consisting of 50%
cerium, 25% lanthanum, 15%
neodymium, and 10% other
rare-earth metals and iron
• Separators
– Polymer with submicron pores
• Electrolyte
– 30% KOH aqueous solution
52
Theoretical Specific Energy
• Nickel metal hydride battery half cell
reactions
NiOOH + H2O + e ↔ Ni(OH)2 + OHEº = 0.45 V
M + H2O + e ↔ MH + OHEº = -0.83 V
• Overall reaction during discharge
NiOOH + MH Ni(OH)2 + M
Eoc = E+ - E- = 0.45 –(-0.83) = 1.28 V
53
Theoretical Specific Energy
• Free energy change (∆G) during discharge
∆G = -nFE = -1 * 96500 * 1.28 = - 123520 J
= -123.5 kJ = -34.3 Wh/mole
• Total weight of reactants
NiOOH + MH Ni(OH)2 + M
NiOOH 92 grams
MH 70 grams
Total weight 162 grams (0.162 kg)/mole
• Theoretical specific energy
34.3 Wh/ 0.162 kg = 212 Wh/kg
• Theoretical energy density
34.3 Wh/0.02 L = 1715 Wh/L
54
Practical Specific Energy
• Practical specific energy up to 45%
theoretical specific energy (212
Wh/kg)up to 90 Wh/kg due to:
– Voltage losses (up to 10%)
– Less inactive weight (~50%)
• Current collectors
• Tabs and terminals
• Solvent (water) in electrolyte
– High utilization of active material (~90%)
55
Effects of Discharge Rate on Capacity
• Capacity least affected by discharge rate
among commonly used batteries (best
abuse tolerance)
Flat discharge voltage curve
C/8 rate
2C rate
4.6 Ah
5.1 Ah
5.6 Ah
6 Ah
56
Outline
• Introduction to batteries
• Equilibrium and kinetics
• Various secondary batteries
Lead acid batteries
Nickel metal hydride batteries
Lithium ion batteries
• Applications
Electric vehicles
Hybrid electric vehicles
57
Lithium Ion Batteries
• Invented by Dr. Goodenough at U. Texas in
1982 and became commercially available in
1991 (Sony)
• Both lithium cobalt oxide and carbon electrodes
are intercalation electrodes
• Have safety issues for applications in HEV and
plug-in HEV
• It is 5 billion dollars industry for applications in
portable electronics (total battery industry ~ 30
billion dollars)
58
Lithium Ion Batteries
• Positive electrodes
– Layered lithium metal oxide (LiMO2, M = cobalt,
nickel, manganese, aluminum, or combination of two
to three metals), spinel lithium manganese oxide
(LiMn2O4), and lithium iron phosphate (LiFePO4) on
aluminum current collector
• Negative electrodes
– Carbon or graphite on copper current collector
• Separators
– Celgard microporous, polyethylene, or ceramic
separators
• Electrolyte
– LiPF6 dissolved in ethylene carbonate (EC)
• Solvent with high dielectric constant (89.6 at 40°C)
• Lithium salt with high conductivity
• 0.005 S/cm as compared to 0.5 S/cm for aqueous electrolyte
59
59
Carbon Negative Electrode
• Prevent lithium metal deposition (or
formation of lithium dendrite)
– Lithium metal deposition could still happen
during rapid charge when Temp < 5°C
– Dendrite could cause short circuit and
thermal runaway
Negative
electrode
Li
metal
Electrolyte
Positive
electrode
Dendrite
60
Lithium Ion Batteries
65
mm
18
mm
Lithium ion battery18650
Alkaline AA battery
3.6 V, 2 Ah
1.5 V, 1.5 Ah
7.2 Wh
2.25 Wh
61
Theoretical Specific Energy
• Lithium ion battery half cell reactions
CoO2 + Li+ + e ↔ LiCoO2
Li
Eº = 1 V
Dendrite
metal
Li+ + C6+ e ↔ LiC6
Eº ~ -3 V
• Overall reaction during discharge
CoO2 + LiC6 LiCoO2 + C6
Eoc = E+ - E- = 1 - (-3.01) = 4 V
62
Theoretical Specific Energy
• Free energy change (∆G) during discharge
∆G = -nFE = -1 * 96500 * 4 = - 386000 J
= -386 kJ = -107.2 Wh/mole
• Total weight of reactants
CoO2 + LiC6 LiCoO2 + C6
CoO2 91 grams
LiC6 79 grams
Total weight 170 grams (0.17 kg)/mole
• Theoretical specific energy
107.2 Wh/ 0.17 kg = 630.6 Wh/kg
• Theoretical energy density
107.2 Wh/0.055 L = 1949 Wh/L
63
Practical Specific Energy
• Practical specific energy up to 30%
theoretical specific energy (630.6
Wh/kg) ~190 Wh/kg due to:
– Voltage losses (up to 10%)
– Less inactive weight (~35%)
•
•
•
•
Current collectors
Tabs and terminals
Electrolyte
Carbon in negative electrode
– Utilization of active material (~50%)
• Intercalation electrodes
64
Charge and Discharge
• Lithium batteries cannot use aqueous
electrolyte
Lithium batteries with aqueous electrolyte
Current
Lithium
ion
battery
~4V
H2
evolution
Water
decomposit
ion voltage
1.23 V
O2
evolution
-3.2 -2.7 -2.2 -1.7 -1.2 -0.7 -0.2 0.3 0.8 1.3 1.8
Voltage (V)
65
Charge
• Overall reaction during charge
LiCoO2 + C6 CoO2 + LiC6
Charge
Li+ + e Li
Carbon
LiCoO2
Lithium
Lithium ion
66
Overcharge
• Positive electrode is oxidized and oxygen
released (exothermic reaction)
67
Discharge
• Overall reaction during discharge
CoO2 + LiC6 LiCoO2 + C6
Discharge
Li Li+ + e
Carbon
LiCoO2
Lithium
Lithium ion
68
Thermal Runaway
• Overcharge
– Exothermic reaction of oxidized positive
electrode material with electrolyte
• High ambient temperature
– SEI (solid electrolyte interphase) decomposition
at temperature 90 to 120 °C
• Short circuit
– Internal
– External
• High charge or discharge current
69
Formation of SEI
• Lithium ion battery is assembled inside a dry
room (does not need a dry box w/inert
atmosphere) with lithium ions impregnated in the
positive electrode (the smaller electrode)
• During the first charge, lithium ions are
transferred from the positive to the negative
electrode and form lithium metal
Enlarged
graphite
particle
-
Graphite
(or C)
particles
CoO2
particles
+
Enlarged
CoO2
particle
Capacity determined by
the positive electrode
Formation of SEI
• The electrolyte, ethylene carbonate (EC), is not
thermodynamically stable with lithium metal
• SEI is formed on carbon or graphite particles
during the first charge (Li active material wasted)
• SEI properties
– SEI has porous structure (more porous if SEI
formation steps are not optimized)
– SEI is ionic conductor (electronic insulator)
ethylene
carbonate
SEI
(Li + EC)
pores
Li-C
Li+ (during
charge)
Li+ + C6+ e ↔ LiC6
Li+ (during
discharge)
71
Thickening of SEI (Failure Mode)
• Charge discharge cycles
– Volume changes in the carbon or graphite
particles crack SEI and expose fresh Li to
electrolyte (EC)
• Storage (calendar life)
– Ethylene carbonate (EC) diffuse through SEI
(pores) and react with Li inside SEI
ethylene
carbonate
SEI
Li-C
pores
Li + EC thicker SEI
(capacity loss & high
impedance rate
capability loss)
72
Advantages and Disadvantages
• Advantages
– Very high energy and power
– Excellent charge retention
• Disadvantages
– Safety concerns
– High cost (control systems)
– Lithium deposition during charge at low
temperature
– Short calendar life
73
New Development
(Positive Electrode)
Structure
Material
Layered
oxides (2D)
LiCoO2
Li(Co-Ni)O2
LiCo1/3Ni1/3Mn1/3O
Eoc
Capacity Safety Cost
3.6 to 151 Ah/kg
3.7
Acceptable
high
LiMn2O4
3.7
119 Ah/kg
good
Low
Olivine (1D) LiFePO4
3.4
161 Ah/kg
best
Low
2
(L-333)
Spinel (3D)
– Spinel is more proven than olivine except a high
temperature
– Spinel has relatively lower capacity (119 vs.150 or 160
Ah/kg for other materials) and solubility problems
– Olivine has very low conductivity
74
New Lithium Iron Phosphate Cells
(CALB, Thunder Sky, GBS)
75
New Development
(Negative Electrode)
• Spinel negative electrode (Altair)
– Lithium titanate (Li4Ti5O12)
• Advantages
– At lower voltage (~ 2.5 V) lithium is
thermodynamically stable in electrolyte no SEI
– Rapid charge and discharge
– Extremely long cycle life (> 20,000)
• Disadvantages
– Lower voltage (2.5 V)
– Low electronic coductivity (additives)
A supercapacitor!
76
Battery V.S. Supercapacitor
Gasoline
77
Battery V.S. Supercapacitor
Supercapacitors VS. Lithium Batteries
Specific power (kW/kg)
30
Commercial supercaps
Apower Cap
25
Nickel-Carbon supercap
Graphene-Based supercap
20
CALB iron phosphate battery
Altair (国轩) titanate battery
15
Fuji Hybrid
10
5
Power Sys
0
0
20
40
60
80
100
120
Spesific energy (Wh/kg)
78
Summary (Three Batteries)
• Lead acid battery
–
–
–
–
Low energy, < 40 Wh/kg
Moderate power, > 200 W/kg
Short life (deep discharge cycle), ~ 400 EV cycles
Low cost, ~ $150/kWh
• Nickel metal hydride battery
–
–
–
–
Moderate energy, < 100 Wh/kg
High power, > 1000W/kg
Long life, ~ 2000 EV cycles
High cost, ~ $1000/kWh (cell)
• Lithium ion battery
–
–
–
–
High energy, < 200Wh/kg
High power, > 1000W/kg
Long life, ~ 2000 EV cycles
High cost, ~ $ 400/kWh (control system)
79
Outline
• Introduction to batteries
• Equilibrium and kinetics
• Various secondary batteries
• Lead acid batteries
• Nickel metal hydride batteries
• Lithium ion batteries
Applications
Electric vehicles
Hybrid electric vehicles
80
Electric Vehicles
• History of electric vehicles
– Electric motor demonstrated in 1832
– Planté invented lead acid batteries in 1860
– Electric vehicles were more popular than
vehicles with internal combustion engines
early 20th century (from 1900 to 1912)
• 30,000 electric vehicles in US
• 200,000 electric vehicle worldwide
– The invention of battery powered starter
(1911) wiped out electric vehicles after 1920
81
Early Electric Vehicle
• Ayrton & Perry EV
(1882)
– Ten lead acid
battery cells (200
pounds)
– Peak power output
400 Watts
– Range 10 ~ 25
miles
– Speed 10 mph
82
Electric Vehicle Speed Record
Jenatzy electric race car sets world speed record at 61 mph
(1899-1902)
83
Electric Vehicles
• Renewed interests on electric vehicles
– Uncertainties on the supply of petroleum
based fuels
– High price of petroleum based fuels
– Improved technologies on batteries
• Global opportunities
– More opportunities in countries such as China
and India
• Less or no crude oil reserves compared to the US
• More city driving
• Shorter range requirements
84
Renewal of Electric Vehicles
Tesla
85
Chinese Electric Vehicles
Build Your Dreams (BYD)
86
GM Chevy Volt
Years in
development:
4
Battery range:
40 miles
Supplemented
by onboard
gas generator
Passengers: 4
Price: $40000
87
Nissan Leaf
Years in
development: 4
Battery range:
100 miles (100%
electric, 0
emissions)
Passengers: 4
Price: $32780
88
Chinese Concept Electric
Vehicles
89
Indian Electric Vehicles
90
USABC Goals for EV Batteries
91
Specific Energy VS Power for
Different Batteries
HEV
Prius
Chevy
Volt
EV
92
Specific Energy VS Power
(with the same capacity)
High Specific Power
Cell
High Specific Energy
Cell
terminal
terminal
terminal
2 tabs
1 tab
+
-
-
+ +
-
-
+ +
+
-
1 tab
2 tabs
terminal
93
Specific Energy VS Power
High Specific Power
High Specific Energy (Range)
•Bias power at the cost of energy
•Bias energy at the cost of power
•Smaller particles, lower density
•Larger particles, higher density
•Thinner electrodes
•Thicker electrodes
•Thicker current collectors (minimize •Thinner current collectors (more
active material)
IR)
94
Battery Design for EV (Example)
• Method I: Estimate force required to move the
vehicle
F = mg*Cr + ½ρCDAv2 + ma + mg*sin(θ)
Cr: coefficient of rolling resistance
CD: Coefficient of air drag
ρ: Density of air
A: Cross section of the vehicle
θ: Slope of the road
• Calculate power and energy required to drive
the vehicle for 200 km
Power P = F * v (velocity)
Energy = ∫P dt
(integration from time t = 0 to T for driving 200 km)
Total energy (Wh) required for the battery pack to drive
200 km
95
Battery Design for EV (Example)
• Use the empirical equation
Range (km) = (Є/e) * Fb
Є: Usable battery specific energy (Wh/kg)
e: Specific weight consumption (Wh/(kg*km))
(e = 0.11 for a normal car driving on flat terrain)
Fb: Battery fraction
• For the battery pack
Є = 150 Wh/kg (lithium ion battery)
Fb = 250 / 1500 = 0.167
Range = (150 / 0.11) * 0.167 = ~ 220 km
(150 Wh/kg * 250 kg = 37.5 kWh)
96
Battery Design for EV (Example)
• Specific weighted consumption
“e”
CONDITIONS
0.06
Well designed, low acceleration rail vehicles, and level conditions
0.07
GM prototype impact with superior aerodynamics but impractical
features
0.09
Stop, start, low acceleration, slow speed bus on level roads,
good weather, stops every 300 m
0.11
For a normal car with all-season tires, generally flat terrain
0.15
Smooth freeway driving, good weather, level terrain
0.20
Hilly terrain
97
Battery Design for EV (summary)
• Energy: ~ 40 kWh for 200 km range
• Power (acceleration): ~ 100 kW , 250kg (400 W/kg)
• Power (regenerative braking): ~ 40 kW (160 W/kg)
• The efficiency of city driving is higher than that of
highway driving
• Weight: battery fraction Fb = 0.167 (less than 1/3
vehicle weight)
• Life: 10 years and 100,000 miles
• Cost: competitive with internal combustion drive
train
98
Outline
• Introduction to batteries
• Equilibrium and kinetics
• Various secondary batteries
• Lead acid batteries
• Nickel metal hydride batteries
• Lithium ion batteries
• Applications
Electric vehicles
Hybrid electric vehicles
99
Introduction
• Hybrid electric vehicle types
Types
Main Attributes
Battery
Micro-1
Stop, power for idle loads, crank ICE
VRLA
Micro-2
Micro-1 plus regenerative braking
VRLA
Mild-1
Micro-2 plus lunch assist
VRLA
Mild-2
Mild-1 plus limited power assist
VRLA, NiMH
Moderate Mild-2 plus full power assist
NiMH
Strong
Moderate plus extended power assist (limited
electric drive)
NiMH
Plug-in
HEV
Strong plus extended electric drive
NiMH, Li-ion
VRLA: Valve regulated lead acid battery
NIMH: Nickel metal hydride battery
100
Battery Design with Higher
Power Output
• Thinner electrodes
and separators
• More electrodes in
parallel
• Shorter aspect ratio
• Thicker and heavier
current collectors
• Conductive additives
mixed with active
materials in
electrodes
101